These are blocks of fine-grained, well-sorted sandstone. They are located adjacent to the abandoned Seneca Quarry, along the C&O Canal in Poolesville, Maryland. This sandstone is distinctly different from the Seneca Red Sandstone that was mined at the Seneca Quarry, indicating that it was quarried elsewhere. Most likely, these blocks were at one point transported to this location from one of the many other now-abandoned quarries along the C&O Canal.